SCPR Integrated SM-SBR Process For Domestic Wastewater Treatment Enhancing Phosphate Removal

Due to high concentration of nitrogen and phosphate, the domestic wastewater general results in eutrophication pouring to water body. With much more attention paid to eutrophication, enhancing the phosphorous removal of domestic wastewater becomes more and more popular. Based on reported researches, side chemical phosphate removal integrated submerged MBR-SBR(SM-SBR) process, SCPR-SM-SBR for short, was designed to enhance the phosphorus removal efficiency. The results were shown in the following:Aluminum sulfate was selected as the coagulant. The method of Response Surface Methodology was used to discuss the effects of two factors of Al/P molar ratio and pH on chemical phosphorus removal, and quadratic model was suggested. At the condition of the pH of anaerobic wasterwater in the range7-8and the removal efficiency above80%, the optimizing Al/P molar ratio was3.26.The effects of pH change of the supernatant after SCPR, the influent COD concentration and the water quality of SCPR on the SM-MBR system was studied. When the supernatant after SCPR was injected into the bioreactor, pH declined to7.6and subsequently recovering to7.9quickly, showing no disturbance on the nitrogen and phosphorus removal.If the COD concentration in the effluent was lower than206mg/L, the TP concentration in the effluent rapidly increased to6.01mg/L at the day of5, the anaerobic phosphate concentration declined from19mg/L to6.13mg/L, losing the steady. At the same time, the ammonia concentration raised to6.16mg/L, corresponding to an increase of TN. Therefore, it was suggested that COD concentration in the influent cannot lower200mg/L, or the COD/P ratio was higher than26. With the enlargement of the SCPR waterflow, the phosphorus removal was significantly enhancing, and the nitrification and denitrification was not inhibited. When QSCPR was40%, TP concentration in the effluent was as lower as0.5mg/L, the average removal efficiency of ammonia and TN were respectively95%and84.6%.Based on the optimization condition, the SCPR-SM-SBR system was operated102d successive. After integrated the stage of SCPR, TP concentration in the effluent was lower 0.5mg/L and the removal rate of TP was above90%.The reduction of ammonia was stable above99%, sometimes the TN removal efficiency was fluctuated, still keeping on average70%. The Independent Sample t-test results indicated that SCPR was beneficial to enhancing phosphate removal efficiency and had no significant negative effect on the growth of PAOs, nitrification and denitrification. The equilibrium analysis of TP in the bioreactor demonstrated that the TP total removal efficiency of93.5%was the combined action of chemical removal efficiency of32.4%and biological removal efficiency of61.05%.With integrated the stage of SCPR, the TMP increased rapidly, accelerating the membrane fouling rate, and the membrane cleaning period was reduced from26days to23days. The viscosity of the sludge mixture increased slowly, to some extent, beneficial for alleviating the membrane fouling. With SEM-EDS analysis on the membrane surface, integrated SCPR led to the increasing of Al3+, Ca2+, Mg2+, Zn2+and Cl", which were important for membrane fouling and could accelerate the fouling rate. Therefore, it was inferred that the reason of increasing membrane fouling rate was the add of membrane load and the acceleration of these trace elements. To relieve the membrane fouling and decrease the washing frequency, N2gas washing was applied in the anaerobic stage. It was showed that the washing period was delayed8days, and the viscosity increasing was promoted, indicating that N2gas washing was positive to weaken the membrane fouling.The analysises of qPCR and DGGE were used to research the effect of SCPR-SM-SBR process on the bacteria community. The relative abundance of amoA related to nitrification was stable, illustrating the high ammonia removal efficiency during the operation straightly.The changes of the relative variances of nirS and nirK related to denitrification were different, but the nitrite reductase was controlled by nirS or nirK, therefore, it was uncertainty of the effect on denitrifying bacteria. The relative abundance of ppK related to aerobic phosphorus uptake increased, indicating the improvement of biological phosphorus removal. The results of PCR-DGGE were shown that, after running the process of SCPR-SM-SBR, the number of nitrifying bacteria (Nitrospira sp.)increased and the number of denitrifying bacteria(Thauera sp.、Dechloromonas sp.、Ferribacterium sp.)was decreased, accounting for the high ammonia removal efficiency and the fluctuated TN removal rate. The Candidatus Accumulibacter sp. was turned to be the dominant bacteria, performing the increasement of biological phosphorus removal. When using N2washing, the nitrifying bacteria(Nitrospira sp.) and denitrifying bacteria(Thauera sp.,Dechloromonas sp.)loss the dominants, possibly owing to higher nitrogen gas concentration inhibiting the denitrifation.